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Continuously-stirred Anaerobic Digester to Convert Organic Wastes into Biogas: System Setup and Basic Operation

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Published on: July 13, 2012

Foaming phenomenon in bench-scale anaerobic digesters.

Amanda M Siebels¹, Sharon C Long

¹Wisconsin State Laboratory of Hygiene, University of Wisconsin, 2601 Agriculture Drive, Madison, Wisconsin 53718, USA.

Water Environment Research : a Research Publication of the Water Environment Federation

|May 24, 2013

Summary

Higher temperatures in anaerobic digesters may worsen foaming issues, contrary to expectations. This study suggests advanced digestion methods like thermophilic or acid phase digestion won't solve Madison's seasonal digester foaming problems.

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Area of Science:

Environmental Engineering
Wastewater Treatment
Anaerobic Digestion

Background:

Madison Metropolitan Sewerage District faces persistent seasonal foaming in anaerobic biosolids digesters.
The precise causes of this foaming remain unidentified.
Existing research offers inconclusive evidence on whether advanced anaerobic digestion processes can mitigate digester foaming.

Purpose of the Study:

To evaluate the impact of thermophilic and acid phase-thermophilic anaerobic digestion configurations on digester foaming.
To compare foaming potential at bench-scale against single-stage mesophilic digestion.
To inform The District's strategies for addressing seasonal foaming issues.

Main Methods:

Utilized bench-scale anaerobic digesters fed with a blend of waste activated sludge (WAS) and primary sludge.
Monitored foaming potential using Alka-Seltzer and aeration tests.
Compared foaming characteristics across mesophilic, thermophilic, and acid phase-thermophilic digestion setups.

Main Results:

Bench-scale acid phase-thermophilic digesters exhibited higher foaming potential compared to mesophilic digesters.
Elevated temperatures appear to increase foaming potential in anaerobic digesters.
Acid phase-thermophilic digestion achieved a 5-10% greater volatile and total solids destruction than mesophilic digestion.

Conclusions:

Switching to thermophilic or incorporating an acid phase in anaerobic digestion is unlikely to resolve The District's full-scale seasonal foaming issues.
Higher operating temperatures may exacerbate foaming problems in wastewater treatment digesters.
While advanced methods improve solids destruction, they do not appear to be a solution for the observed foaming.